1) Field of the Invention
The present invention relates to a method whereby a processing unit, which is connected through a common data bus to a plurality of devices for controlling these devices or for performing control operations through the use of these devices, recognizes connection states of the devices, and further to a processing unit having a device connection state recognizing function, to which this method is applied.
2) Description of the Related Art
FIG. 28 is a block diagram showing an example of configuration of a system in which a plurality of devices are connected to a general processing unit. In FIG. 28, a processing unit 100 is in connection with a plurality of devices, such as an LCD (Liquid Crystal Display) 121, a RAM 122 and a ROM 123. The connection between these LCD 121, RAM 122 and ROM 123, and the processing unit 100 is made through a common 8-bit data bus 110 comprising data signal lines DT0 to DT7, and, additionally, the LCD 121, the RAM 122 and ROM 123 are connected to the processing unit 100 through signal lines 111a, 111b, 111c for the interchange of address signals, control signals and others, respectively.
Furthermore, the processing unit 100 supplies a display control signal through the signal line 111a to the LCD 121, and sends display data through the data bus 110 to the LCD 121, thereby executing the display control on the LCD 121. Still further, the processing unit 100 sends address signal or a write/readout instruction signal through the signal line 111b to the RAM 122 to thereby control the data write into the RAM 122 or the data readout from the RAM 122. Moreover, the processing unit 100 forwards an address signal or a readout instruction signal through the signal line 111c to the ROM 123 to thereby control the data readout from the ROM 123.
Meanwhile, a system, shown in FIG. 29, is equivalent to the removal of the ROM 123 from the system shown in FIG. 28, and is in connection with an LCD 121 and a RAM 122 which form devices.
While the difference between the system shown in FIG. 28 and the system shown in FIG. 29 is the device connection state to the processing unit 100, usually the processing unit 100 does not have a means to detect and recognize such a device connection state difference (that is, the devices connected to the processing unit 100).
Thus, it would be considered that signal lines dedicated to detection are provided so that the processing unit 100 bears a means for detecting the presence or absence of the devices.
However, in the case of the method of recognizing a device connection state with the installation of the signal lines dedicated to detection, if the number of devices to be connected to a processing unit increases, the number of signal lines dedicated to detection increases accordingly, and if, for example, the processing unit is an integrated circuit, the increase in the number of signal lines on a chip requires high density wiring of the signal lines, which leads to a rise of cost. For this reason, a desire exist that the device connection state can be recognized without the addition of the signal lines dedicated to detection.
Meanwhile, a computer system for use in various kinds of application is equipped with a plurality of devices according to these applications, with these devices being placed under control of a processing unit (control integrated circuit or the like). In such a system, in order to control various types of devices, a ROM previously retains drivers/handles (device control programs) to devices connected, and a CPU constituting the processing unit reads out and starts the drivers/handlers from the ROM at the starting of the system.
For instance, as FIG. 30A shows, a hardware 200, bearing four devices D1, D3, D4 and D8, previously contains a ROM 210 retaining four drivers/handlers (device control programs) for taking charge of control of these devices D1, D3, D4 and D8. In this case, at the starting of the system, a CPU in the hardware, as shown in FIG. 30B, successively reads out the drivers/handlers for the four devices D1, D3, D4 and D8 from the ROM 210 and starts them (see steps A11 to A14).
Furthermore, as FIG. 31A shows, a hardware 201, being equipped with six devices D1, D2, D3, D4, D7 and D8, internally has a ROM 211 previously retaining six drivers/handlers (device control programs) for controlling these devices D1 to D4, D7 and D8. In this instance, as shown in FIG. 31B, at the starting of the system, a CPU in the hardware 201 successively reads out the drivers/handlers for the six devices D1 to D4, D7 and D8 from the ROM 211 to start them (see steps A21 to A26).
In like manner, as FIG. 32A shows, a hardware 202, including two devices D7 and D10, contains a ROM 212 previously storing two drivers/handlers (device control programs) for controlling these devices D7 and D10. In this case, as shown in FIG. 32B, at the activation of the system, a CPU in the hardware 202 successively reads out the drivers/handlers for the two devices D7 and D10 from the ROM 212 to activate them (see steps A31, A32).
In case where each computer system employs a different connection state of devices as noted above, there is a need to prepare a ROM conforming to the devices of each computer system.
In general, the devices to be connected to various types of computer systems are not always different from each other at every service, but are common thereto in many cases. For instance, the different devices are limited to some types such as a keyboard, a printer, an IC (Integrated Circuit) card in addition to the LCD, the RAM and the ROM mentioned above. That is, some are selected from these devices and connected thereto.
Thus, it would be considered to prepare a general-purpose ROM previously storing drivers/handlers for all devices which may be connected to computer systems and to, at the activation of a system, recognize the devices connected to that system so that the drivers/handlers (device control programs) for the devices recognized are read out from the general-purpose ROM and put to activation. For instance, as far as the examples shown in FIGS. 30 to 32 is, the general-purpose ROM to be provided is one storing all the drivers/handlers (device control programs) for the devices D1 to D10. This can eliminate the need for preparing a different ROM for each computer system, which saves troubles to be taken in storing programs in the ROM and simplifies the management of parts, thereby contributing to the reduction of system manufacturing cost.
However, in the conventional ways, since the processing unit does not have a means to recognize the devices connected thereto as mentioned above, irrespective of the employment of a versatile ROM, difficulty is experienced in reading out only the required drivers/handlers (device control programs) for their start.
In addition, if signal lines dedicated to detection for recognizing the device connection states are provided in order to make the general-purpose ROM available, as mentioned before, this results in the increase/higher density in the signal lines on a chip, and in its turn leads to higher cost. Accordingly, a stronger desire exists that the recognition of the device connection state is feasible with no additional signal lines dedicated to detection.
The present invention has been developed in consideration of this situation, and it is therefore an object of this invention to provide a device connection state recognizing method and a processing unit having a device connection state recognizing function, which are capable of recognizing the device connection state without adding signal lines dedicated to detection.
For this purpose, in accordance with this invention, there is provided a device connection state recognizing method by which a processing unit exhibiting an ability to have connection through a common data bus to a plurality of devices recognizes a device connection state, comprising the steps of previously connecting a portion of or all of a plurality of data signal lines constituting the data bus through a pull-up resistor to a high electric potential or connecting them through a pull-down resistor to a low electric potential in accordance with a connection state of the devices, and making the processing unit read, as structure information data, a high electric potential state/low electric potential state generated by the pull-up resistor/pull-down resistor in a portion of or all the plurality of data signal lines to recognize the device connection state on the basis of the structure information data read.
In addition, in accordance with this invention, there is provided a processing unit having a device connection state recognizing function and exhibiting an ability to have connection through a common data bus to a plurality of devices, in a state where a portion of or all of a plurality of data signal lines constituting the data bus are connected through a pull-up resistor to a high electric potential or connected through a pull-down resistor to a low electric potential in accordance with a connection state of the devices, the processing unit comprising a recognizing section for reading, as structure information data, a high electric potential state/low electric potential state generated by the pull-up resistor/pull-down resistor in a portion of or all the plurality of data signal lines to recognize the device connection state on the basis of the structure information data read.
With the device connection state recognizing method and the processing unit having a device connection state recognizing function according to this invention, in a manner of reading, as structure information data, a high electric potential state/low electric potential state generated by a pull-up resistor/pull-down resistor in data signal lines constituting a data bus, a device connection state becomes recognizable without the addition of signal lines dedicated to detection. That is, it does not rely on the addition of signal lines dedicated to detection to use a general-purpose ROM mentioned before. This eliminates the need for the provision of a different ROM at every computer system, which clears away the troubles needed for putting a program in a ROM along with simplifying the parts management, thus contributing to the reduction of system manufacturing cost.